Put the two best players in the world – Magnus Carlsen and Levon Aronian – together in a tournament with World Champion Viswanathan Anand and one may expect the rest of the field to be mere extras.

However after the first half of the Grand Slam Final, played in a glass cube in Sao Paulo's famous Ibirapuera Park, the US-born Italian Fabiano Caruana has shown – for the third time in three months – that he can compete with, and beat, the world's elite players.

Unperturbed by some of the coldest spring weather that Sao Paulo locals could remember, Caruana, 20, knocked over Carlsen, 21, in the first round and Russia's hope Sergey Karjakin, 22, in the second.

As the players prepare to fly to Bilbao in northern Spain for the second half of the Grand Slam Final, Caruana is a full point ahead of Aronian (or four points using the tournament's 3-1-0 soccer scoring system) and a point and a half ahead of Anand and Carlsen.

The Grand Slam Final may be one of the strongest tournaments of 2012 but its raison d'etre has almost completely collapsed.

When the Grand Slam Association began four years ago, tournaments were falling over themselves to join up, with only the Sparkassen tournament in Dortmund and the Tal Memorial in Moscow staying aloof.

The established traditional tournaments in Wijk aan Zee and Linares were joined by new super-tournaments in Sofia, Nanjing and Bazna for a circuit where the winners could form a worthy Grand Slam final in Bilbao. (Soon Bilbao was to share the final; first with Shanghai and then in 2011 and 2012 with Sao Paulo.)

Though fine in theory, the Grand Slam Final has been dogged by bad luck. In the 2009/10 season Magnus Carlsen won all but one Grand Slam tournament, making any Grand Slam Final something of an absurdity.

More worryingly, year by year the Grand Slam tournaments ran into financial difficulties and dropped out of the circuit.

In 2011 one of the jewels in the Grand Slam crown, Linares, stopped after being one of the world's elite tournaments for three decades. (With 40% unemployment in Andalucia, the chance of the tournament resuming in the near future appears bleak. The mayor of Linares, a big chess supporter, is currently locked in a car factory with the factory workers, trying to prevent Volkswagen from closing down their workplace.)

By 2012, only one Grand Slam tournament remained, Wijk aan Zee, so the organizers required some creative thinking to create a Final for a circuit which no longer existed.

The solution was ingenious – invite the winners from the super-tournaments that had not agreed to become part of the Grand Slam circuit!

Thus the 2012 Grand Slam Final features Carlsen (Tal Memorial winner), Aronian (winner of Wijk aan Zee), plus Caruana and Karjakin, joint winners of Dortmund 2012. Add the winner of the 2012 World Championship match, Viswanathan Anand, and the Grand Slam Final magically became a serious end-of-season event. (The only top player missing is Vladimir Kramnik (winner of the 2011 London Classic), because the former World Champion refuses to play in tournaments split between continents.)

Yet despite so many elite GMs being present, the armchair critics, with computer programs such as Houdini running by their side, have been scathing about the number of errors made by the competitors in Sao Paulo.

The biggest howls of disapproval came in the fourth round, when the two top players in the world were going head to head...

Sao Paulo Grand Slam Final Round 4

White: M.Carlsen

Black: L.Aronian

Carlsen is well ahead on the clock – 40 minutes to 13 – and the Norwegian world number one later explained that with his knight impregnable on e4, he felt he had little to fear.

26.Qd1 Qh3 27.Bf4!?

Played after 11 minutes thought. Aronian briefly looked at 27...R8xf4!? 28.gxf4 Nxf4 and saw that it was refuted by 29.Ra8+ Kh7 30.Ng5+. So, knowing that serious time trouble in Sao Paulo – a tournament where there was no increment on the first time control – could be fatal, Aronian quickly replied

27...Bc3!?

with the aim of making the previous variation playable by decoying the knight away from control of g5.

However by now every chess computer was screaming out that 27...R8xf4! would have won, since after 28.gxf4 Nxf4 29.Ra8+ Black has 30...Bf8! and mate will be forced after 31.Rg1 Qxh2+!!

32.Kxh2 Rh3.

Carlsen admitted that he saw this immediately after he moved and was shaking for the rest of the game, which concluded

Yet, something even worse was avoided by mere chance a round earlier...

Aronian vs. Vallejo, Photo Cathy Rogers

Sao Paulo Grand Slam Final Round 3

White: L.Aronian

Black: F.Vallejo

Here Vallejo, running short of time, took a repetition of moves with

30...Ra1+ 31.Kg2 Ra2+ 32.Kf1 Ra1+ 33.Kg2 Ra2+ and the game was drawn.

Vallejo admitted that he had also been tempted to play 30...Qxh2, which would oblige Aronian to force a draw with 31.Rg7+ Kxg7 32.Qe7+ when Black cannot escape the checks.

At the post-game press conference, Brazilian GM Gilberto Milos pointed out that 30...Qxh2 would actually have allowed 31.Ne5+!! fxe5 32.Rc7+, with mate to follow.

Vallejo looked shocked that he had almost walked into this, but Aronian was equally surprised, since he had intended 31.Rg7+ and was not at all sure that he would have noticed the forced mate. "I saw that I was making a draw," said Aronian, "but maybe I would see it."

"Actually, I was very lucky," admitted Vallejo," since I was not sure whether to force a draw or let him do so with 30...Qxh2 31.Rg7+."

On the same day, another large tactical accident was missed

Sao Paulo Grand Slam Final Round 3

White: M.Carlsen

Black: S.Karjakin

Black has just played 45...f5 - "My only chance because otherwise White just brings his king to c2 and plays Rb3," explained Karjakin.

46.Rd5

"Perhaps I should play 46.f3," but I believed that after the exchange of rooks White should be very close to winning here," said Carlsen.

After the game commentator Gilberto Milos, having had a little help from his silicon friend, pointed out the extraordinary trick missed by both player after 46. Rd5

Position after 46. Rd5

46...Rxb2!! 47.Nxb2 fxe4! when the White rook is trapped and White will struggle to draw.

Analysis after 47...fxe4

"Oh! Really! 46...Rxb2 is brilliant!” exclaimed Karjakin.

"Wow!" was all Carlsen could manage.

So are the top players playing worse that they used to? Would superstars of old have missed such tactical ideas?

Absolutely. The problem, as Shakespeare pointed out many years ago, is not in the stars but in ourselves.

We are living in an age where everybody has access to computer assessments, meaning that every small oversight by top players appears magnified.

In years past, tricks such as 46...Rxb2+!! might only have been noticed months or even years later, perhaps only brought to light by an amateur writing a letter to Larry Evans in Chess Life.

Nowadays every move of the top Grandmasters can be challenged and yes, being human, even Carlsen and Aronian can miss moves that seem obvious once you are shown them.

After all, who would see 46...Rxb2+!! without a computer pointing it out?

Fabiano Caruana – that's who! (Did I mention that Caruana was in good form?) Yes, Caruana was wandering past Carlsen's game against Karjakin, when Karjakin played 45...f5. At first Caruana was puzzled as to why Karjakin would allow 46.Rd5, which obliges Black to exchange rooks into a likely losing ending, when he saw 46...Rxb2+!! and thought “What a great trap by Karjakin!”. Sadly Caruana's faith in the genius of Karjakin was disabused one move later.

To conclude one trick that neither the players nor the spectators saw...

Sao Paulo Grand Slam Final Round 2

White: F.Vallejo

Black: M.Carlsen

Vallejo thought that he was holding with

31.Rc1 Rxc1 32.Kxc1 but after 32...h4!!

Carlsen wins by force. Vallejo was expecting only 32...a5 33.Nc2 when 33...Bxc2 34.Kxc2 leads only to a draw.

However nobody noticed the computer move 33.Rd8!! in this variation, which leaves Black scrambling to force a draw.

Yet there was one place where the players were fully appreciated – at Ibirapuera Park in Sao Paulo. Every day 300-400 spectators surrounded the glass box where the world's best were caged, watching the games and listening to commentators Gilberto Milos and Susan Polgar.

Spectators in Sao Paulo, Photo Cathy Rogers

Without the tyranny of the computer assessments, the players ideas were admired and appreciated by the commentators and the fans.

The players did their part, participating in post-game press conferences win or lose, while also posing for multiple photos with fans – no doubt soon to be displayed as a modern form of autograph on Facebook.

At the conclusion of the Sao Paulo half of the Grand Slam Final, Gilberto Milos made a point of thanking each of the players for coming to Brazil and competing hard and fearlessly.

The thanks were amplified by the audience with rousing rounds of applause but the biggest was reserved for the Caruana after his near-death experience in a five hour marathon against Aronian. The crowd appreciated the world's best but realised that they may have seen a new star born.